[dmj+@andrew.cmu.edu: Re: C++ debugging progress]

[Daniel Jacobowitz <drow@mvista.com>]

Feh.  Meant to send this to the lists.

----- Forwarded message from Daniel Jacobowitz <dmj+@andrew.cmu.edu> -----

Date: Wed, 28 Nov 2001 15:18:19 -0500
From: Daniel Jacobowitz <dmj+@andrew.cmu.edu>
Subject: Re: C++ debugging progress
To: Jason Merrill <jason@redhat.com>

On Wed, Nov 28, 2001 at 07:40:37PM +0000, Jason Merrill wrote:
> >>>>> "Daniel" == Daniel Jacobowitz <drow@mvista.com> writes:
> 
> > On Wed, Nov 28, 2001 at 09:31:07AM +0000, Jason Merrill wrote:
> 
> >> So you're using the inheritance information in the RTTI rather than the debug
> >> info?  That seems unfortunate.  I'm not sure why you would need to worry
> >> about ordering; the debug info should tell you exactly where things are.
> >> If it doesn't, it should probably be fixed.
> 
> > In that case, the debug info absolutely needs to be fixed.
> 
> >  <1><22e>: Abbrev Number: 15 (DW_TAG_structure_type)
> >      DW_AT_sibling     : <2df>  
> >      DW_AT_name        : Left   
> >      DW_AT_byte_size   : 12     
> >      DW_AT_decl_file   : 1      
> >      DW_AT_decl_line   : 2      
> >      DW_AT_containing_type: <22e>       
> >  <2><23f>: Abbrev Number: 22 (DW_TAG_inheritance)
> >      DW_AT_type        : <56>   
> >      DW_AT_data_member_location: 2 byte block: 23 8 (DW_OP_plus_uconst: 8; )
> >      DW_AT_virtuality  : 1      (virtual)
> >      DW_AT_accessibility: 1     (public)
> 
> Yep.  Since Base is a virtual base of Left, the DW_AT_data_member_location
> here should be a complex expression telling the debugger to go through the
> vtable.  I'll get on it.

Thanks!

> I'll also change the stabs output to give the offset within the vtable
> rather than the offset of the base in a complete object; gdb will still
> need to be clever enough to know what to do with it.

<delete lots of incoherent rambling>

OK, if I'm reading this at all correctly, the offset in the baseclass
definition is assumed to be 0 for a virtual baseclass, and ignored; it
is assumed that there will be a $vb later.  So that offset slot is a
perfect place to put the information I need.  Just let me know if it is
relative to the start of the vtable or to the vtable pointer.  That'll
be enough information to do a much better job.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer

----- End forwarded message -----

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer